Transactional memory operation success rate

ABSTRACT

Embodiments of the invention are directed to methods for handling cache prefetch requests. The method includes receiving a request to prefetch data from main memory to a cache. The method further includes based on a determination that the prefetch request is a speculative prefetch request, determining if the cache is being used for transactional memory. The method further includes based on a determination that the cache is not being used for transactional memory, processing the prefetch request. The method further includes based on a determination that the cache is being used for transactional memory, and a determination if the prefetch request can be processed without affecting transactional memory, processing the prefetch request. The method further includes based on a determination that the cache is being used for transactional memory, and a determination if the prefetch request can be processed without affecting transactional memory, rejecting the prefetch request.

BACKGROUND

The present invention relates in general to the field of computing. Morespecifically, the present invention relates to systems and methodologiesfor improving the success rate of transactional memory operations.

Computer systems that allow multiple concurrently executing threadssometimes allow access to shared memory location. Writing multi-threadedprograms can be difficult due to the complexities of coordinatingconcurrent memory access. One approach to controlling concurrent accessis the use of transactional memory. In a transactional memory system, asection of code can be designated to be a transaction. The transactionexecutes atomically with respect to other threads of execution withinthe transactional memory system. For example, if the transactionincludes two memory write operations, then the transactional memorysystem ensures that all other threads may only observe the cumulativeeffects of both memory operations or of neither, but not the effects ofonly one memory operation.

Current implementations of transactional memory limit the number ofcache lines (transaction footprint) in a transaction for severaldifferent reasons. A transaction is aborted if the core sends outadditional cache line requests that are not related to the transactionsthat will force the eviction of transaction cache lines from the caches,thus impacting the performance of the transaction.

SUMMARY

Embodiments of the present invention are directed to a method forhandling cache prefetch requests. The method includes receiving arequest to prefetch data from main memory to a cache. The method furtherincludes based on a determination that the prefetch request is aspeculative prefetch request, determining if the cache is being used fortransactional memory. The method further includes based on adetermination that the cache is not being used for transactional memory,processing the prefetch request. The method further includes based on adetermination that the cache is being used for transactional memory, anda determination if the prefetch request can be processed withoutaffecting transactional memory, processing the prefetch request. Themethod further includes based on a determination that the cache is beingused for transactional memory, and a determination if the prefetchrequest can be processed without affecting transactional memory,rejecting the prefetch request.

Embodiments of the present invention are further directed to a computersystem handling cache prefetch requests. The computer system includes acache memory and a processor system communicatively coupled to the cachememory. The processor system is configured to perform a method. Themethod includes receiving a request to prefetch data from main memory toa cache. The method further includes based on a determination that theprefetch request is a speculative prefetch request, determining if thecache is being used for transactional memory. The method furtherincludes based on a determination that the cache is not being used fortransactional memory, processing the prefetch request. The methodfurther includes based on a determination that the cache is being usedfor transactional memory, and a determination if the prefetch requestcan be processed without affecting transactional memory, processing theprefetch request. The method further includes based on a determinationthat the cache is being used for transactional memory, and adetermination if the prefetch request can be processed without affectingtransactional memory, rejecting the prefetch request.

Embodiments of the present invention are further directed to a designstructure embodied in a machine-readable storage medium for designing,manufacturing, or testing an integrated circuit. The design structurecomprises includes a cache memory and a processor system communicativelycoupled to the cache memory. The processor system is configured toperform a method.

The method includes receiving a request to prefetch data from mainmemory to a cache. The method further includes based on a determinationthat the prefetch request is a speculative prefetch request, determiningif the cache is being used for transactional memory. The method furtherincludes based on a determination that the cache is not being used fortransactional memory, processing the prefetch request. The methodfurther includes based on a determination that the cache is being usedfor transactional memory, and a determination if the prefetch requestcan be processed without affecting transactional memory, processing theprefetch request. The method further includes based on a determinationthat the cache is being used for transactional memory, and adetermination if the prefetch request can be processed without affectingtransactional memory, rejecting the prefetch request.

Additional features and advantages are realized through techniquesdescribed herein. Other embodiments and aspects are described in detailherein. For a better understanding, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter that is regarded as embodiments is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe embodiments are apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 depicts an overview of a data processing system according toembodiments of the invention;

FIG. 2 depicts a more detailed block diagram flow diagram of a dataprocessing system according to embodiments of the invention;

FIG. 3 depicts a flow diagram illustrating a situation that can occurwith shared memory;

FIG. 4 depicts a flow diagram illustrating the operation of atransactional memory system;

FIG. 5 depicts a flow diagram illustrating the operation of one or moreembodiments; and

FIG. 6 depicts a data flow diagram illustrating a design process.

DETAILED DESCRIPTION

Various embodiments of the present invention will now be described withreference to the related drawings. Alternate embodiments can be devisedwithout departing from the scope of this invention. Various connectionsmight be set forth between elements in the following description and inthe drawings. These connections, unless specified otherwise, can bedirect or indirect, and the present description is not intended to belimiting in this respect. Accordingly, a coupling of entities can referto either a direct or an indirect connection.

Additionally, although a detailed description of a computing device ispresented, configuration and implementation of the teachings recitedherein are not limited to a particular type or configuration ofcomputing device(s). Rather, embodiments are capable of beingimplemented in conjunction with any other type or configuration ofwireless or non-wireless computing devices and/or computingenvironments, now known or later developed.

Furthermore, although a detailed description of usage with specificdevices is included herein, implementation of the teachings recitedherein are not limited to embodiments described herein. Rather,embodiments are capable of being implemented in conjunction with anyother type of electronic device, now known or later developed.

At least the features and combinations of features described in theimmediately present application, including the corresponding featuresand combinations of features depicted in the figures amount tosignificantly more than implementing a method of managing transactionalmemory. Additionally, at least the features and combinations of featuresdescribed in the immediately following paragraphs, including thecorresponding features and combinations of features depicted in thefigures go beyond what is well understood, routine and conventional inthe relevant field(s).

Shared memory occurs in computing systems that have multiple threadsand/or multiple cores and/or multiple users. An exemplary issue that canoccur with shared memory is when two different processes attempt to reador write the same memory location simultaneously.

To provide an exemplary, simplified situation, refer to the flowchart ofFIG. 3. imagine a program that updates a bank balance. The bank balancestarts at $1,000 (block 302). Process A and Process B simultaneouslyperform. Process A reads the bank balance (block 310), then updates thebank balance by withdrawing $100 (block 312) and writing the new balance(block 314). Process B reads the bank balance (block 320), then attemptsto update the bank balance by depositing $200 (block 322) and writingthe new balance (block 324).

If Process A and Process B occur sequentially in either order, theresult is a balance of $1,100 ($1,000−$100+$200). However, if block 220occurs after block 210 but prior to block 210, then Process B reads thebalance value before Process A has finished. The result is that bothProcess A and Process B attempt to write at the same time, then both areadding or subtracting the value from the same balance value. The resultis either a failure to write or the wrong value is written into the bankbalance feed.

One method of addressing such a situation is the use of a lock. WhenProcess A reads the balance, it locks the memory address of the balance.Therefore, Process B cannot read the balance can obtain incorrectinformation. Once Process A is finished with its task, it unlocks thememory address, which allows Process B to perform.

While such a process can solve the problem of two processessimultaneously reading or writing the same memory location, otherproblems can be caused by such a lock procedure. For example, overheadis incurred by the use of the locks, Process B might sit idle whilewaiting for the release of a lock, and the potential of a deadlock,where two processes are waiting for the other process to release a lockin order to perform a particular function. Because both processes aredependent on each other, the deadlock prevents either process fromfinishing. While a case of two processes can be relatively simple toavoid a deadlock, a multi-threaded or multi-processor machine can makeit more difficult to avoid the deadlock. There are other shortcomings oflocking. These shortcomings can include the possibility of a deadlockwhen a given thread holds more than one lock and prevents the forwardprogress of other threads. In addition, there is a performance cost tolock acquisition which might not have been necessary because noconflicting accesses would have occurred.

One type of memory system that addresses such problems is transactionalmemory. Transactional memory simplifies parallel programming by groupingread and write operations and performing them like a single operation.Transactional memory is like database transactions where all sharedmemory accesses and their effects are either committed all together ordiscarded together as a group. All threads can enter the critical regionsimultaneously. If there are conflicts in accessing the shared memorydata, threads try accessing the shared memory data again or are stoppedwithout updating the shared memory data. Therefore, transactional memorycan be considered lock-free synchronization. A traditional lock schemewould involve a process locking a memory location, performing operationson the locked memory location, and then releasing the lock. In contrast,a transactional scheme involves a process declaring a memory location tobe atomic, then performing transactions on a copy of the memorylocation. Upon completion of the process, the processor (also known as acentral processing unit or CPU) determines if there are any conflicts.If there are conflicts, then transaction fails and has to try again.However, if there are no conflicts, then the transaction succeeds andthe memory changes are made permanent. An advantage of transactionalmemory is that if there is no direct conflict between two memorylocations, then two processes can operate in parallel, instead of havingto wait for a lock to be released. The memory locations involved in thetransaction can be called a transaction footprint.

With continued reference to FIG. 3, in a transactional memory system,process A, comprising blocks 310, 312, and 314, is considered onetransaction and process B, comprising block 320, 322, and 324, isconsidered a second transaction. Process A copies the bank balance to afirst temporary memory location, then completes blocks 312 and 314.Process B copies the bank balance to a second temporary memory location,then completes blocks 312 and 314. After Process A is complete, itdetermines if any other action was taken with respect to the bankbalance. If not, then the new bank balance is written to the permanentmemory location. However, if after Process A completes, it turns outthat Process B has not completed, then Process A is aborted and has tostart again. In such a manner, there is no overwriting of data by otherprocesses and there is no need to perform a memory lock.

A flowchart illustrating method 400 is presented in FIG. 4. Method 400is merely exemplary and is not limited to the embodiments presentedherein. Method 400 can be employed in many different embodiments orexamples not specifically depicted or described herein. In someembodiments, the procedures, processes, and/or activities of method 400can be performed in the order presented. In other embodiments, one ormore of the procedures, processes, and/or activities of method 400 canbe combined or skipped. In one or more embodiments, method 400 isperformed by a processor as it is executing instructions.

Method 400 is a simplified flowchart illustrating the operation oftransactional memory. It should be understood that other implementationsof transactional memory are possible. A sequence of operations begins(block 402). A set of memory locations are copied to a “scratch” ortemporary memory location (block 404). These are considered thetransactional memory locations. Operations are then performed on thescratch memory locations (406). After the transaction block is finishedprocessing, it is determined if the set of transactional memorylocations are being operated upon by another sequence (block 408). Sucha determination can occur using a form of transactional memory logic.The transactional memory logic includes entries that indicate whichareas of memory are being used for transactional memory. If thedetermination shows that the memory locations are not being used, thenthe transaction is finalized by committing the scratch memory to the setof memory locations (block 410). Otherwise, the transaction is abortedand started again (block 412).

With reference to both FIG. 3 and FIG. 4, if Process A completes beforeProcess B ever begins, then block 410 will execute. However, if ProcessB starts after Process A starts, but before it finishes, block 412 willoccur for Process A because, from the perspective of Process A, thememory location is in use. However, Process B might finish and commitprior to Process A re-starting.

Thus, it can be seen that there are some advantages to transactionalmemory. The overhead of obtaining a memory lock was prevented andProcess B was not required to remain idle while waiting for a memorylock to be released. While this was a simplified example showing onlytwo processes running on two cores, if you have multiple paralleloperations which access a data structure, all of which are capable ofwriting to it, but few of which actually do, then lock-based memorysynchronization may require that all such operations be run serially toavoid the chance of data corruption. Transactional memory can allowalmost all the operations to be executed in parallel, only losingparallelism when some process actually does write to the data structure.

A cache is a set of small, fast area of memory that a processor uses toprocess data more quickly. Because cache memory is faster than systemmemory, a processor can access cache memory more quickly and thus not beburdened by a slow system memory.

Cache memories are commonly utilized to temporarily buffer memory blocksthat might be accessed by a processor in order to speed up processing byreducing access latency introduced by having to load needed data andinstructions from slower system memory. In some embodiments, the levelone (L1) cache is associated with one particular processor core andcannot be accessed by other cores. Typically, in response to a memoryaccess instruction such as a load or store instruction, the processorcore first accesses the directory of the upper-level cache. If therequested memory block is not found in the upper-level cache, theprocessor core can then access lower-level caches such as level 2 (L2)or level 3 (L3) caches or system memory for the requested memory block.The lowest level cache (L3 in some embodiments, level 4 (L4) or level 5(L5) in other embodiments) is often shared among several processorcores.

With reference to FIG. 1, there is illustrated a high-level blockdiagram depicting an exemplary data processing system 100 in accordancewith one embodiment. In the depicted embodiment, data processing system100 is a cache-coherent symmetric multiprocessor (SMP) data processingsystem including multiple processing nodes 102 a, 102 b for processingdata and instructions. Processing nodes 102 are coupled to a systeminterconnect 110 for conveying address, data and control information.System interconnect 110 may be implemented, for example, as a busedinterconnect, a switched interconnect or a hybrid interconnect.

In the depicted embodiment, each processing node 102 is realized as amulti-chip module (MCM) containing four processing units 104 a-104 d,each preferably realized as a respective integrated circuit. Theprocessing units 104 within each processing node 102 are coupled forcommunication to each other and system interconnect 110 by a localinterconnect 114, which, like system interconnect 110, may beimplemented, for example, with one or more buses and/or switches. Systeminterconnect 110 and local interconnects 114 together form a systemfabric.

As described below in greater detail with reference to FIG. 2,processing units 104 each include a memory controller 106 coupled tolocal interconnect 114 to provide an interface to a respective systemmemory 108. Data and instructions residing in system memories 108 cangenerally be accessed, cached and modified by a processor core in anyprocessing unit 104 of any processing node 102 within data processingsystem 100. System memories 108 thus form the lowest level of volatilestorage in the distributed shared memory system of data processingsystem 100. In alternative embodiments, one or more memory controllers106 (and system memories 108) can be coupled to system interconnect 110rather than a local interconnect 114.

Those skilled in the art will appreciate that SMP data processing system100 of FIG. 1 can include many additional non-illustrated components,such as interconnect bridges, non-volatile storage, ports for connectionto networks or attached devices, etc. Because such additional componentsare not necessary for an understanding of the described embodiments,they are not illustrated in FIG. 1 or discussed further herein. Itshould also be understood, however, that the enhancements describedherein are applicable to cache coherent data processing systems ofdiverse architectures and are in no way limited to the generalized dataprocessing system architecture illustrated in FIG. 1.

Referring now to FIG. 2, there is depicted a more detailed block diagramof an exemplary processing unit 104 in accordance with one embodiment.In the depicted embodiment, each processing unit 104 is an integratedcircuit including two or more processor cores 200 a, 200 b forprocessing instructions and data. In a preferred embodiment, eachprocessor core 200 is capable of independently executing multiplehardware threads of execution simultaneously. However, in the followingdescription, unless the interaction between threads executing on a sameprocessor core is relevant in a particular context, for simplicity,terms “processor core” and “thread executing on a processor core” areused interchangeably. As depicted, each processor core 200 includes oneor more execution units, such as load-store unit (LSU) 202, forexecuting instructions. The instructions executed by LSU 202 includememory access instructions that request load or store access to a memoryblock in the distributed shared memory system or cause the generation ofa request for load or store access to a memory block in the distributedshared memory system. Memory blocks obtained from the distributed sharedmemory system by load accesses are buffered in one or more registerfiles (RFs) 208, and memory blocks updated by store accesses are writtento the distributed shared memory system from the one or more registerfiles 208.

The operation of each processor core 200 is supported by a multi-levelvolatile memory hierarchy having at its lowest level a shared systemmemory 108 accessed via an integrated memory controller 106, and at itsupper levels, one or more levels of cache memory, which in theillustrative embodiment include a store-through level one (L1) cache 226within and private to each processor core 200, and a respective store-inlevel two (L2) cache 130 for each processor core 200 a, 200 b. In orderto efficiently handle multiple concurrent memory access requests tocacheable addresses, each L2 cache 130 can be implemented with multipleL2 cache slices, each of which handles memory access requests for arespective set of real memory addresses.

Although the illustrated cache hierarchies includes only two levels ofcache, those skilled in the art will appreciate that alternativeembodiments may include additional levels (L3, L4, etc.) of on-chip oroff-chip, private or shared, in-line or lookaside cache, which may befully inclusive, partially inclusive, or non-inclusive of the contentsthe upper levels of cache.

Each processing unit 104 further includes an integrated and distributedfabric controller 216 responsible for controlling the flow of operationson the system fabric comprising local interconnect 114 and systeminterconnect 110 and for implementing the coherency communicationrequired to implement the selected cache coherency protocol. Processingunit 104 further includes an integrated I/O (input/output) controller214 supporting the attachment of one or more I/O devices (not depicted).

In operation, when a hardware thread under execution by a processor core200 includes a memory access instruction requesting a specified memoryaccess operation to be performed, LSU 202 executes the memory accessinstruction to determine the target address (e.g., an effective address)of the memory access request. After translation of the target address toa real address, L1 cache 226 is accessed utilizing the target address.Assuming the indicated memory access cannot be satisfied solely byreference to L1 cache 226, LSU 202 then transmits the memory accessrequest, which includes at least a transaction type (ttype) (e.g., loador store) and the target real address, to its affiliated L2 cache 130for servicing.

It will also be appreciated by those skilled in the art that accesslatency can be improved by prefetching data that is likely to accessedby a processor core 200 into one or more levels of the associated cachehierarchy in advance of need. Accordingly, processing unit 104 caninclude one or more prefetch engines, such as prefetch engine (PFE) 212,that generate prefetch load requests based on historical demand accesspatterns of processor cores 200.

With prefetching, instead of retrieving data from system memory exactlywhen it is needed, a prediction is made as to what data will be neededin the future. Based on the prediction, data is fetched from systemmemory 108 to L2 cache 230 a or 230 b (or sometimes directly to L1 cache226). If L2 cache 230 a is full when prefetch data is written to it,part of the L2 cache 230 a is overwritten with the new prefetch data.

A cache is written to in increments that is sometimes referred to as a“cache line.” The number of cache lines in a cache depends on both thesize of the cache line (typically between 4 and 64 bytes) in addition tothe size of the cache.

A problem can occur when cache is used in conjunction with transactionalmemory. As described above, in transactional memory, a portion of memoryis copied to a temporary memory, operations are performed on thetemporary memory, then the temporary memory is committed to main memoryif certain conditions are met (such as the memory locations not beingused by other processes).

In some instances, a portion of memory is copied into an area of L2cache 230 a for use as the scratch memory. Therefore, when prefetch datais retrieved from system memory 108 into L2 cache 230 a, it is possiblethat data in L2 cache 230 a that is being overwritten is thetransactional memory data. Overwriting transactional memory will resultin the failure of the transactional memory operation, requiring theoperation to be executed again, slowing down the processing speed ofprocessor 100.

Embodiments of the present invention address the above-described issuesby using a novel method and system to handle interactions between acache and transactional memory. An analysis is performed to determinethe type of prefetch being requested. In the case of a speculativeprefetch, if the speculative prefetch will result in a transactionalmemory portion being overwritten or evicted, then the prefetch is notcompleted. Otherwise, the prefetch will occur.

A flowchart illustrating method 500 is presented in FIG. 5. Method 500is merely exemplary and is not limited to the embodiments presentedherein. Method 500 can be employed in many different embodiments orexamples not specifically depicted or described herein. In someembodiments, the procedures, processes, and/or activities of method 500can be performed in the order presented. In other embodiments, one ormore of the procedures, processes, and/or activities of method 500 canbe combined or skipped. In one or more embodiments, method 500 isperformed by a processor as it is executing instructions.

A request is received to prefetch data from main memory to cache (block502). The prefetch request can be generated in one of a variety ofdifferent manners. In one or more embodiments, the processorautomatically generates prefetch requests based on a variety ofcriteria, in an attempt to speed up the processor by guessing as towhich data will be used by a processor.

The request is analyzed to determine if it involves any transactionalmemory (block 504). If not, then this process ends (block 512) and othermethods can be used to handle the prefetch request. The request isanalyzed to determine if it is a demand prefetch or a speculativeprefetch (block 506).

In some embodiments, cache prefetches can broadly be categorized intotwo categories, demand prefetches (also known as a demand load or ademand request), and speculative prefetches (also known as a speculativeexecution fetch). A demand prefetch occurs when a cache needs specificdata to be transferred from main memory to cache memory to execute aninstruction, such as a “next to complete” instruction. A speculativeprefetch occurs when the request for a transfer of data to betransferred from main memory to the cache is only predicted to be neededand has not been specifically requested. These can be, for example, theresult of a conditional branch prediction. In a conditional branchprediction, a prediction is made as to which branch is to be taken.Thereafter, memory is retrieved based on the prediction. If theprediction is correct, then the next instruction has already beenfetched. If the prediction is wrong, the next instruction has to beretrieved. However, until a conditional branch actually resolves,instructions after the conditional branch may be considered to bespeculative.

The determination of whether a request is a demand prefetch or aspeculative prefetch can be performed in a variety of different manners.In some embodiments, a hardware prefetcher (such as prefetch engine 212)is coupled to a load/store unit (such as LSU 202) within a processor orprocessor core (such as processor core 200 a). At the time theprefetcher issues a prefetch request, it may know whether the request isa demand prefetch or a speculative prefetch. Thus, a prefetch requestmay be accompanied by a notification (such as a single bit) thatindicates which type of prefetch is being requested. In someembodiments, an analysis is performed to determine if the prefetch is ademand prefetch or a speculative prefetch. Many methods can be used toperform such an analysis, both those now known and those developed inthe future.

If the request is a demand prefetch, the prefetch occurs (block 508). Nocheck is performed with respect to transactional memory. Even if theprefetch will result in a failure due to an eviction of thetransactional memory from the cache, the prefetch still occurs. Theresult will be the failure of any transaction that use the transactionalmemory that is evicted. If the request is a speculative prefetch, thenan additional analysis is performed.

It is determined if the prefetch will result in the eviction of aportion of transactional memory (block 510). This can be accomplished ina number of different manners. For example, the cache can be examined todetermine if there will be any data that will be evicted. This caninvolve determining the size of the prefetch request and the size of thetransactional memory. From that data, it can be determined how muchinformation can be safely removed from the cache without affectingtransactional memory (for example, determining if there is informationin the cache that is no longer needed). Transactional memory logicwithin a processor can be used to perform such a determination.Transactional memory logic includes entries that indicate which cachelines are included in a transaction footprint.

If the prefetch can occur without evicting data that is needed fortransactional memory, the operation can proceed with block 508, becausethe transactional memory is not affected by the prefetch request.

If the size of the prefetch request is greater than the amount that canbe safely removed from the cache, that means some data will be evictedfrom the cache. It is determined if data can be evicted from the cachewithout affecting the transactional memory (block 512). In someinstances, a portion of the cache can be chosen to be evicted ahead ofthe portion of cache that is reserved for transactional memory. Only ifit is not possible to save the portion of cache reserved fortransactional memory will the prefetch request be dropped (block 514).In all other situations, the prefetch can be performed (block 508).

With reference now to FIG. 6, there is depicted a block diagram of anexemplary design flow 600 used for example, in semiconductor IC logicdesign, simulation, test, layout, and manufacture. Design flow 600includes processes, machines and/or mechanisms for processing designstructures or devices to generate logically or otherwise functionallyequivalent representations of the design structures and/or devicesdescribed above. The design structures processed and/or generated bydesign flow 600 may be encoded on machine-readable transmission orstorage media to include data and/or instructions that when executed orotherwise processed on a data processing system generate a logically,structurally, mechanically, or otherwise functionally equivalentrepresentation of hardware components, circuits, devices, or systems.Machines include, but are not limited to, any machine used in an ICdesign process, such as designing, manufacturing, or simulating acircuit, component, device, or system. For example, machines mayinclude: lithography machines, machines and/or equipment for generatingmasks (e.g. e-beam writers), computers or equipment for simulatingdesign structures, any apparatus used in the manufacturing or testprocess, or any machines for programming functionally equivalentrepresentations of the design structures into any medium (e.g. a machinefor programming a programmable gate array).

Design flow 600 may vary depending on the type of representation beingdesigned. For example, a design flow 600 for building an applicationspecific IC (ASIC) may differ from a design flow 600 for designing astandard component or from a design flow 600 for instantiating thedesign into a programmable array, for example a programmable gate array(PGA) or a field programmable gate array (FPGA).

FIG. 6 illustrates multiple such design structures including an inputdesign structure that is preferably processed by a design process 610.Design structure 620 may be a logical simulation design structuregenerated and processed by design process 610 to produce a logicallyequivalent functional representation of a hardware device. Designstructure 620 may also or alternatively comprise data and/or programinstructions that when processed by design process 610, generate afunctional representation of the physical structure of a hardwaredevice. Whether representing functional and/or structural designfeatures, design structure 620 may be generated using electroniccomputer-aided design (ECAD) such as implemented by a coredeveloper/designer. When encoded on a machine-readable datatransmission, gate array, or storage medium, design structure 620 may beaccessed and processed by one or more hardware and/or software moduleswithin design process 610 to simulate or otherwise functionallyrepresent an electronic component, circuit, electronic or logic module,apparatus, device, or system such as those described above. As such,design structure 620 may comprise files or other data structuresincluding human and/or machine-readable source code, compiledstructures, and computer-executable code structures that when processedby a design or simulation data processing system, functionally simulateor otherwise represent circuits or other levels of hardware logicdesign. Such data structures may include hardware-description language(HDL) design entities or other data structures conforming to and/orcompatible with lower-level HDL design languages such as Verilog andVHDL, and/or higher level design languages such as C or C++.

Design process 610 preferably employs and incorporates hardware and/orsoftware modules for synthesizing, translating, or otherwise processinga design/simulation functional equivalent of the components, circuits,devices, or logic structures shown above to generate a netlist 680 whichmay contain design structures such as design structure 620. Netlist 680may comprise, for example, compiled or otherwise processed datastructures representing a list of wires, discrete components, logicgates, control circuits, I/O devices, models, etc. that describes theconnections to other elements and circuits in an integrated circuitdesign. Netlist 680 may be synthesized using an iterative process inwhich netlist 680 is resynthesized one or more times depending on designspecifications and parameters for the device. As with other designstructure types described herein, netlist 680 may be recorded on amachine-readable storage medium or programmed into a programmable gatearray. The medium may be a non-volatile storage medium such as amagnetic or optical disk drive, a programmable gate array, a compactflash, or other flash memory. Additionally, or in the alternative, themedium may be a system or cache memory, or buffer space.

Design process 610 may include hardware and software modules forprocessing a variety of input data structure types including netlist680. Such data structure types may reside, for example, within libraryelements 630 and include a set of commonly used elements, circuits, anddevices, including models, layouts, and symbolic representations, for agiven manufacturing technology (e.g., different technology nodes, 32 nm,45 nm, 90 nm, etc.). The data structure types may further include designspecifications 640, characterization data 650, verification data 660,design rules 670, and test data files 685 which may include input testpatterns, output test results, and other testing information. Designprocess 610 may further include, for example, standard mechanical designprocesses such as stress analysis, thermal analysis, mechanical eventsimulation, process simulation for operations such as casting, molding,and die press forming, etc. One of ordinary skill in the art ofmechanical design can appreciate the extent of possible mechanicaldesign tools and applications used in design process 610 withoutdeviating from the scope and spirit of the invention. Design process 610may also include modules for performing standard circuit designprocesses such as timing analysis, verification, design rule checking,place and route operations, etc.

Design process 610 employs and incorporates logic and physical designtools such as HDL compilers and simulation model build tools to processdesign structure 620 together with some or all of the depictedsupporting data structures along with any additional mechanical designor data (if applicable), to generate a second design structure 690.Design structure 690 resides on a storage medium or programmable gatearray in a data format used for the exchange of data of mechanicaldevices and structures (e.g., information stored in a IGES, DXF,Parasolid XT, JT, DRG, or any other suitable format for storing orrendering such mechanical design structures). Similar to designstructure 620, design structure 690 preferably comprises one or morefiles, data structures, or other computer-encoded data or instructionsthat reside on transmission or data storage media and that whenprocessed by an ECAD system generate a logically or otherwisefunctionally equivalent form of one or more of the embodiments of theinvention shown above. In one embodiment, design structure 690 maycomprise a compiled, executable HDL simulation model that functionallysimulates the devices shown above.

Design structure 690 may also employ a data format used for the exchangeof layout data of integrated circuits and/or symbolic data format (e.g.,information stored in a GDSII (GDS2), GL1, OASIS, map files, or anyother suitable format for storing such design data structures). Designstructure 690 may comprise information such as, for example, symbolicdata, map files, test data files, design content files, manufacturingdata, layout parameters, wires, levels of metal, vias, shapes, data forrouting through the manufacturing line, and any other data required by amanufacturer or other designer/developer to produce a device orstructure as described above and shown above. Design structure 690 maythen proceed to a stage 695 where, for example, design structure 690:proceeds to tape-out, is released to manufacturing, is released to amask house, is sent to another design house, is sent back to thecustomer, etc.

Aspects of various embodiments are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to variousembodiments. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer-readable program instructions.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams can represent a module, segment, or portionof instructions, which includes one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block can occur out of theorder noted in the figures. For example, two blocks shown in successioncan, in fact, be executed substantially concurrently, or the blocks cansometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a”, “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willbe further understood that the terms “comprises” and/or “comprising,”when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, element components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescriptions presented herein are for purposes of illustration anddescription, but is not intended to be exhaustive or limited. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of embodiments ofthe invention. The embodiments were chosen and described in order tobest explain the principles of operation and the practical application,and to enable others of ordinary skill in the art to understandembodiments of the present invention for various embodiments withvarious modifications as are suited to the particular use contemplated.

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 8. A computer system for handling cacheprefetch requests, the system comprising: a cache memory; and aprocessor system communicatively coupled to the cache memory; theprocessor system configured to: receive a request to prefetch data froma main memory to a cache; and based on a determination that the prefetchrequest is a speculative prefetch request, determine if the cache isbeing used for transactional memory; based on a determination that thecache is not being used for transactional memory, process the prefetchrequest; based on a determination that the cache is being used fortransactional memory, and a determination if the prefetch request can beprocessed without affecting transactional memory, process the prefetchrequest; and based on a determination that the cache is being used fortransactional memory, and a determination if the prefetch request can beprocessed without affecting transactional memory, rejecting the prefetchrequest.
 9. The computer system of claim 8 wherein the processor systemis further configured to: based on a determination that the prefetchrequest is not a speculative prefetch request, processing the prefetchrequest.
 10. The computer system of claim 8 wherein the determinationthat the prefetch request can be processed without affectingtransactional memory comprises: determining a size of the prefetchrequest; and determining that the size of the prefetch request issmaller than a size of available cache memory.
 11. The computer systemof claim 10 wherein the determination that the prefetch request can beprocessed without affecting transactional memory further comprises:based on a determination that the size of available cache memory issmaller than the size of the prefetch request, determining a size ofinformation that can be removed from cache memory without affectingtransactional memory; if the size of the prefetch request is less than asize of information that can be removed from cache memory withoutaffecting transactional memory, then the prefetch request can beprocessed without affecting transactional memory.
 12. The computersystem of claim 10 wherein determining the size of information that canbe removed from cache memory without transactional memory is based atleast in part on determining a size of the transactional memory.
 13. Thecomputer system of claim 8 wherein processing the prefetch requestcomprises: determining an area of cache to remove; moving information inthe prefetch request from main memory to the area of cache to remove.14. The computer system of claim 8 wherein the determination that theprefetch request will result in an eviction is based at least in part ondetermining the size of the prefetch request.
 15. A design structuretangibly embodied in a machine-readable storage medium for designing,manufacturing, or testing an integrated circuit, the design structurecomprising: a cache memory; and a processor core coupled to the cachememory, the processor core configured to: receive a request to prefetchdata from a main memory to a cache; and based on a determination thatthe prefetch request is a speculative prefetch request, determine if thecache is being used for transactional memory; based on a determinationthat the cache is not being used for transactional memory, process theprefetch request; based on a determination that the cache is being usedfor transactional memory, and a determination if the prefetch requestcan be processed without affecting transactional memory, process theprefetch request; and based on a determination that the cache is beingused for transactional memory, and a determination if the prefetchrequest can be processed without affecting transactional memory,rejecting the prefetch request.
 16. The design structure of claim 15wherein the processor core is further configured to: based on adetermination that the prefetch request is not a speculative prefetchrequest, processing the prefetch request.
 17. The design structure ofclaim 16 wherein the determination that the prefetch request can beprocessed without affecting transactional memory comprises: determininga size of the prefetch request; and determining that the size of theprefetch request is smaller than a size of available cache memory. 18.The design structure of claim 17 wherein the determination that theprefetch request can be processed without affecting transactional memoryfurther comprises: based on a determination that the size of availablecache memory is smaller than the size of the prefetch request,determining a size of information that can be removed from cache memorywithout affecting transactional memory; if the size of the prefetchrequest is less than a size of information that can be removed fromcache memory without affecting transactional memory, then the prefetchrequest can be processed without affecting transactional memory.
 19. Thedesign structure of claim 17 wherein determining the size of informationthat can be removed from cache memory without transactional memory isbased at least in part on determining a size of the transactionalmemory.
 20. The design structure of claim 15 wherein processing theprefetch request comprises: determining an area of cache to remove;moving information in the prefetch request from main memory to the areaof cache to remove.